One technique for transmitting actuation forces to the moveable segments of articulating instruments involves the use of a cable within a housing or a coil tube. This arrangement is commonly referred to as a Bowden cable and is similar in operation to a brake system on bicycle. This cable is used to transmit an actuation force from a control handle out to a steerable active segment. In some cases the forces needed to maneuver a steerable instrument can be large. In some cases, the large actuation force results from friction between the steel cable and the coil tube. It is desirable to reduce the amount of force the frictional forces in the cable/tube arrangement including the use of lubricants such as, for example, molybdenum disulfide.
However useful the lubricants may be, a number of practical challenges remain, such as, for example: (1) the molybdenum disulfide lubricant in powder form will eventually wear out with use of the scope causing degradation of scope performance; (2) the molybdenum disulfide lubricant is difficult to apply inside the coil and is messy during application; (3) the addition of any lubricant between cable and coil tube also causes lubrication issues between each of the coils of the coil tube allowing them to slip over each other under compressive loads. Coil tube buckling rapidly degrades endoscope performance and require expensive rebuilt of the scope coils.
What is needed is an improved way of overcoming the friction forces associated with transmitting actuation forces to the moveable segments of an articulating instrument. strand non-metallic braid while maintaining the diameter of the bonded area the same as or less than the diameter of either the non-metallic multi-strand braid or the lead line. Next, advance the multi-strand non-metallic braid through a coil tube using the lead line. In one alternative, the lead line is altered before the bonding step to improve adhesion to the non-metallic multi-strand braid. In another alternative, the bonding step includes gluing one end of the lead line to one end of a multi-strand non-metallic braid. In another alternative, the bonding step includes thermally bonding one end of the lead line to one end of a multi-strand non-metallic braid. In one aspect, a strand of the multi-strand braid is cut before the bonding step. In another embodiment, before the bonding step, placing one end of the lead line and one end of the non-metallic multi-strand braid into a fixture. In one aspect, the diameter of one end of the lead line or one end of the non-metallic multi-strand braid is reduced before bonding the lead line and the non-metallic multi-strand braid. In one aspect, the lead line is formed from the same material as the non-metallic multi-stranded braid.
In another aspect, the end of the multi-strand non-metallic braid is terminated. In one aspect, terminating includes forming a knot in the multi-strand non-metallic braid. In another aspect, the multi-strand non-metallic braid is passed through a threaded element before the terminating step. Termination may be accomplished by applying an adhesive to the knot formed in the multi-strand non-metallic braid, gluing a ball within the multi-strand non-metallic braid, securing a crimp to the multi-strand non-metallic braid or forming a loop in one end of the multi-strand non-metallic braid.
In another embodiment, there is provided a steerable instrument having a plurality of hinged segments; a multi-strand non-metallic braid connected distally to one segment of the plurality of segments and proximally to an actuator; and a steering controller adapted to control the actuator to move the hinged segment using the multi-strand non-metallic braid. In one aspect, a connector assembly couples the multi-strand non-metallic braid to the actuator. In another aspect, there is a carriage assembly in the connector and attached to one end of the multi-strand non-metallic braid. In another aspect, the multi-strand non-metallic braid passes through a coil tube extending between the connector assembly and the segment. In one alternative, the ratio of the clearance between the multi-strand non-metallic braid and the interior surface of the coil tube to the inner diameter of the coil tube is less than or equal to 15%. In one embodiment, the multi-strand non-metallic braid comprises ultra high molecular weight polyethylene (UHMWPE). In one aspect, the multi-strand non-metallic braid is connected distally to one segment of the plurality of segments by terminating the multi-strand non-metallic braid at the desired segment. In another aspect, there is a threaded element on the one end of the multi-strand non-metallic braid to attach the one end of the multi-strand non-metallic braid to the carriage assembly. In another aspect, there is a knot formed in the multi-strand non-metallic braid positioned between the threaded element on the one end of the multi-strand non-metallic braid and the carriage assembly. In one embodiment, there is a knot formed in the multi-strand non-metallic braid. In one aspect, there is an adhesive applied to the knot. In another aspect, the adhesive contains a pigment that provides a visual indication that the adhesive is present.